The subject of the present invention is a device for injecting a medicament in liquid form at controlled flow rate into an ambulant. In the case of certain treatments, it is necessary to inject a liquid medicament at a very low flow rate for a very long period of time. To avoid having to immobilize the patient, it is known practice for the patient to be fitted with a device which injects at a controlled flow rate, which he carries around on his person and with which he can move around.
One known device comprises an elastic cuff made of silicone or latex forming a reservoir, contained inside a rigid chamber. A device of this kind has an inlet to allow the medicament to be injected into the elastic cuff using a syringe. This inlet is fitted with a non-return valve preventing the medicament from flowing out once the syringe has been disconnected. The medicament outlet towards the patient is via a second orifice of calibrated cross section. This orifice is connected to a line with which the patient is infused. When the patient is connected, the medicament flows with a flow rate which depends on the pressure generated by the calibrated cuff, on the cross section of the outlet orifice and on the viscosity of the liquid. A device of this kind on the one hand requires the use of a syringe to fill it and, on the other hand, does not infuse at a constant flow rate, especially when emptying the last third of the elastic cuff.
The object of the invention is to provide a device which injects at controlled flow rate, which does not require an intermediate syringe for filling it, which provides a constant infusion flow rate and which also allows the value of this flow rate to be adjusted.
To this end, the device to which the invention relates comprises:
a syringe body equipped with an access which may be connected in succession to a filling member, such as a needle, and to an infusion line fitted with a non-return valve to allow liquid to pass from the syringe into the line,
a housing mounted so that it can slide in leaktight fashion inside the body so as to vary the volume of a chamber which it delimits with the body of the syringe,
an element which, forming a piston, mounted on the housing and in contact with the chamber, is able, according to its position, to create a raised pressure or reduced pressure in the chamber,
automatic control means for moving the piston-forming element back and forth.
Initially, to fill the chamber, liquid is drawn in like in a conventional syringe, the sliding housing acting as a piston.
At a later stage, the syringe body is connected to an infusion line and the piston-forming element is actuated, successively creating a raised pressure and a reduced pressure in the chamber containing the liquid medicament. When a raised pressure is exerted, a certain amount of liquid is discharged through the infusion line, whereas when a reduced pressure is exerted by the piston, the housing moves in the body of the syringe in a direction which reduces the volume of the chamber, thus automatically adapting to the volume of liquid contained therein.
According to one advantageous embodiment of the invention, the housing contains an electromagnet with which there is associated a moving core plunger mounted so that it can slide in a bore opening in the face of the housing delimiting the chamber, the moving core plunger being moved in one direction by the electromagnet and in the opposite direction by return means.
In this case a sealing diaphragm is mounted between the end of the moving core plunger and the chamber.
The means of returning the moving core plunger consist of a spring, and the means for controlling the electromagnet consist of an electric pulse generator. It is possible to vary the duration and the frequency of the pulses by controlling the pulse generator using an oscillator generating a signal whose frequency is preset using a potentiometer.
Advantageously, the means of moving the piston-forming element are housed in the housing.
According to another feature of the invention, the end of the syringe body lying at the opposite end to the access is open and serves as a passage for an operating member in the form of a plunger mounted on the rear wall of the housing.
The plunger is not fitted until the phase of filling the body of the syringe, and is then removed for the infusion operation.
Advantageously, it is the removal of the plunger which causes the infusion device to begin operation.
To this end, mounted on the rear wall of the housing is a switch, placed in the supply circuit of the means for controlling the electromagnet, this switch being actuated by the plunger so as to deactivate the means for controlling the electromagnet when the plunger is fixed on the housing, and vice versa.
In order to prevent the sliding housing from moving back inside the body when the piston exerts a raised pressure inside the chamber, the housing has means preventing it from moving backwards during injection periods.
According to one embodiment, the means preventing the housing from moving backwards during injection periods consist of radial tabs fixed on the rear wall of the housing, facing outwards and intended to brace against the interior face of the body.
As the piston body has to be able to move backwards so that the syringe body can be filled, when the plunger is mounted, the tabs preventing the backwards movement have a number of successive inverse undulations, the free end of each tab being inclined backwards, and the plunger, when mounted on the housing, presses against a central undulation of each tab so as to uncouple the tabs from the wall of the syringe body.
According to another feature of the invention, the infusion line is equipped with an accumulator situated downstream of the non-return valve. The role of this accumulator is to instantly absorb the volume expelled upon each pulse, then to return the stored liquid to the patient. Its usefulness is all the greater, when the infusion line is of small diameter, because of pressure drops. This accumulator may consist of a simple elastic chamber.